/*****************************************************************************
* FILE: dotprod_mutex.c
* DESCRIPTION:
* This example program illustrates the use of mutex variables
* in a threads program. This version was obtained by modifying the
* serial version of the program (dotprod_serial.c) which performs a
* dot product. The main data is made available to all threads through
* a globally accessible structure. Each thread works on a different
* part of the data. The main thread waits for all the threads to complete
* their computations, and then it prints the resulting sum.
*
* SOURCE: Vijay Sonnad, IBM
* LAST REVISED: 9/20/98 Blaise Barney
******************************************************************************/
#include
#include
#include
/*
The following structure contains the necessary information
to allow the function "dotprod" to access its input data and
place its output into the structure. This structure is
unchanged from the sequential version.
*/
typedef struct
{
double *a;
double *b;
double sum;
int veclen;
} DOTDATA;
/* Define globally accessible variables and a mutex */
#define NUMTHRDS 4
#define VECLEN 100
DOTDATA dotstr;
pthread_t callThd[NUMTHRDS];
pthread_mutex_t mutexsum;
/*
The function dotprod is activated when the thread is created.
As before, all input to this routine is obtained from a structure
of type DOTDATA and all output from this function is written into
this structure. The benefit of this approach is apparent for the
multi-threaded program: when a thread is created we pass a single
argument to the activated function - typically this argument
is a thread number. All the other information required by the
function is accessed from the globally accessible structure.
*/
void *dotprod(void *arg)
{
/* Define and use local variables for convenience */
int i, start, end, offset, len ;
double mysum, *x, *y;
offset = (int)arg;
len = dotstr.veclen;
start = offset*len;
end = start + len;
x = dotstr.a;
y = dotstr.b;
/*
Perform the dot product and assign result
to the appropriate variable in the structure.
*/
mysum = 0;
for (i=start; i